1. Field of the Invention
The present general inventive concept relates to an inkjet printer head. More particularly, the present general inventive concept relates to a thermal-driving type inkjet printer head that sprays ink by using bubbles formed when the ink are heated, and a method to manufacture the same.
2. Description of the Related Art
In general, an inkjet image forming apparatus includes an inkjet printer head that sprays ink based on image signals. The inkjet printer head discharges ink droplets based on the image signals to print characters and figures on a print medium. The image forming apparatuses are classified into a shuttle type image forming apparatus, in which the printer head sprays ink while reciprocating in a transfer direction (sub-scanning direction) and an orthogonal direction of the print medium, and an array type image forming apparatus, in which the printer head has a length corresponding to a width of the print medium and thus can perform line printing.
The inkjet printer head may be classified into a thermal-driving type inkjet printer head and a piezoelectric-driving type inkjet printer head according to an ink spraying scheme thereof. The thermal-driving type inkjet printer head includes a heating member that is disposed in an ink chamber and sprays ink droplets through a nozzle by using an expansive force of bubbles formed when the heating member heatsink in the ink chamber. The piezoelectric-driving type inkjet printer head includes piezoelectric member that sprays ink droplets through a nozzle by using pressure applied to ink when the piezoelectric member is transformed by supplied voltage.
FIG. 1 is a sectional view schematically illustrating the conventional thermal-driving type inkjet printer head and FIG. 2 is a SEM (scanning electron microscope) photograph partially illustrating the construction of the conventional thermal-driving type inkjet printer head.
As illustrated in FIGS. 1 and 2, the conventional inkjet printer head includes a silicon substrate 11, a plurality of insulating layers 12 to 15 on the silicon substrate 11, a heating member 16 on an uppermost insulating layer 15, an electrode 17 on the heating member 16, a chamber layer 18 on the electrode 17, and a nozzle layer 19 on the chamber layer 18, in which the electrode 17 supplies power to the heating member 16, the chamber layer 18 forms an ink chamber 21, and the nozzle layer 19.
According to such a conventional inkjet printer head, if pulse type current is applied to the heating member 16 through the electrode 17, heat is generated in the heating member 16 and ink adjacent to the heating member 16 are heated. As the ink is heated and boiled, bubbles are formed and expanded to apply pressure to ink filled in the ink chamber 21. Accordingly, ink in a lower portion of the nozzle 22 is sprayed through the nozzle 22 in the form of droplets.
Ideal pulse type current is not always applied to such a conventional thermal-driving type inkjet printer head. That is, when the inkjet printer head is used, a pulse of the electric current applied to the inkjet printer head may irregularly change according to various factors. With the change in the pulse of the electric current applied to the inkjet printer head, a spraying speed of the ink droplets changes and thus the printing quality may be degraded. In order to maintain a constant spraying speed of the ink droplets regardless of the change in the pulse of the applied electric current, the heating member 16 having a large resistance, for example, is used.
Since the resistance of the heating member 16 may be calculated by an equation (R=ρ(L/S)), several methods capable of increasing the resistance of the heating member 16 through the equation can be derived.
In the equation, ρ denotes specific resistance of material constituting the heating member, S denotes a sectional area of the heating member in a flowing direction of electric current, and L denotes a length of the heating member.
The heating member 16 includes material having a large specific resistance, so that the resistance of the heating member 16 can be increased. However, since the well-known material suitable for the heating member 16 is limited, new material must be found. Thus, a development period inevitably increases.
Next, the length of the heating member 16 is increased, so that the resistance of the heating member 16 can be increased. However, as the length of the heating member 16 increases, a bubble generation area is widened. Thus, the heat of the heating member 16 is dispersed instead of being concentrated on the ink in the lower portion of the nozzle 16, so efficiency of the heating member 16 may deteriorate.
Finally, a thickness of the heating member 16 is decreased to reduce the sectional area thereof, so that the resistance of the heating member 16 can be increased. However, as the thickness of the heating member 16 is decreased, durability of the heating member 16 is degraded.
As described above, according to the conventional inkjet printer head in which the heating member 16 is flatly located in the lower portion of the nozzle 22, the resistance of the heating member 16 is not easily increased.
Further, since the thickness between the heating member 16 and the substrate 11 is thick, the heat generated in the heating member 16 is not quickly emitted and accumulated in the inkjet printer head. That is, since the insulating layers 12 to 15 between the heating member 16 and the substrate 11 have poor heat conductivity, the heat generated when the heating member 16 operates is not quickly emitted and continuously accumulated in the inkjet printer head. In order to cause the ink droplets to be stably sprayed, when electric current flows in the heating member 16, the temperature of the heating member 16 increases to a high temperature (e.g. 300° C.) and bubbles must be formed, However, when electric current does not flow in the heating member 16, the temperature of the heating member 16 decreases and bubbles must be contracted to allow ink to be quickly introduced into the ink chamber 21.
According to the conventional inkjet printer head as described above, if the heat of the heating member 16 is not easily emitted, bubbles are not quickly contracted after the ink droplets are sprayed and thus ink may not be easily supplied to the ink chamber 21. Therefore, enhancing a printing speed by increasing a frequency of the electric current supplied to the heating member 16 is difficult.